Lighting systems (such as headlights) are well-known and are used in a wide variety of applications, including automotive applications. In general, a lighting system includes an apparatus for emitting one or more distinct light patterns. For example, a lighting system may emit light in a low-beam pattern/mode in which light is generally emitted below the horizon. The lighting system may also emit light in a high beam pattern/mode in which light is generally emitted above and below the horizon.
Recent headlamp performance testing procedures, in particular photometric output requirements, make it difficult for manufactures to comply. Non-exhaustive examples of applicable regulations/testing procedures are described by the United States National Highway Traffic Safety Administration (NHTSA) (e.g., at pages 96-99 and Tables XVIII, XIX-a of the Department of Transportation (DOT) 49 C.F.R. Parts 564 and 571 (which correspond to Vol. 72, No. 232 (Dec. 4, 2009) pages 68328-68331 of the Federal Register), hereinafter referred to as the NHTSA standard). In general, the requirements and/or testing procedures specify sharper gradient cutoffs, wider spreads, and reduced glare to oncoming traffic.
One conventional way to produce a headlamp beam is a reflection system in which the light of the source bulb is distributed by the shape of the reflector and use of a shading cup placed in front of the bulb to prevent uncontrolled direct beam being emitted by the bulb. In reflection systems, a clear cover lens, which is otherwise optically insignificant, is mounted forward of a reflector to prevent moisture or dirt from reaching the bulb or reflector. The reflector is smooth, segmented, or faceted; the beam distribution is exclusively produced by the reflector geometry and the shading cap.
Another, qualitatively different other way to produce a sharp gradient cutoff is through the use of a “projector” or “projection” type headlamp. The light from the bulb source is first focused by a nearly elliptical reflector in the focal plane of the lens. Projector headlamp designs involve light from the reflector passing by a shutter (also referred to as shade or shield) that blocks or subtracts light out of the pattern to produce a sharp gradient cutoff before passing the light to a projector lens. A shutter, when present, generates a low beam pattern. Some shutters are fixed (non-movable); other shutters are movable between two positions that change the pattern from low beam to high beam by removing the blocking effect of the shutter. Examples of shutters in projector headlamps are seen in Pat. Pub. US 2009/0052200 (Tessnow) and U.S. Pat. No. 8,070,339 (Koike) at FIG. 7 therein described as prior art. Examples of other headlamps are shown in U.S. Pat. No. 9,150,144 (Abe); U.S. Pat. No. 9,068,710 (Lai); and U.S. Pat. No. 8,523,417 (Kobayashi).